1. Field of the Invention
The present invention relates to a laundry dryer, and more particularly, to a laundry dryer having a gas combustion apparatus employing a flame holder for separating the flame exiting a mixing pipe.
2. Discussion of the Related Art
A typical laundry dryer performs drying using hot air, which is drawn into a drying chamber through an inlet duct, under the power of a blower installed adjacent an outlet pipe, to be discharged from the drying chamber via a lint-filtering unit. The hot air may be generated by means of an electric heater or gas combustion. A gas dryer employs a gas combustion apparatus.
Referring to FIG. 1, illustrating major components of a gas-combustion laundry dryer according to a related art, a cylindrical drum 1 together with front and rear supports 7 and 9 essentially establishes a drying chamber 5 in which drying is performed. A blower 17 is powered to discharge the drying air from the drum 1 via an outlet assembly 13 including a lint filter 14, which are installed on the front side of the front support 7, and a lint duct 15 receiving the lint filter and communicating with the outlet assembly. The blower 17, mounted within a blower housing 18, is connected to the lint duct 15 and draws air from the drying chamber 5 for discharge via an outlet pipe 19 communicating with the blower housing.
An air inlet duct 12, installed on the rear side of the rear support 9 to communicate with the drying chamber 5, supplies hot air to the drying chamber. One end of a guide funnel 20 is tapered for connection to the inlet duct 12 at its entrance hole to guide hot air into the inlet duct.
Referring to FIG. 2, the other end (mouth) of the guide funnel 20 receives a length of a mixing pipe 24 for mixing primary air, i.e., external air entering through the inlet end of the mixing pipe, with gas injected from a gas nozzle 2. Thus, the outlet of the mixing pipe 24 extends a predetermined distance into the mouth of the guide funnel 20 while the gas nozzle 22, under the control of a valve 30, is disposed at its inlet to inject gas into the mixing pipe. The valve 30 thus controls the amount of gas introduced to the gas nozzle 22 via a gas supply pipe 23, which is connected a gas supply source (not shown). Accordingly, the gas from the gas nozzle 22 is controllably mixed with the primary air in a mixing passage 240 of the mixing pipe 24, which has a tapered circular cross-section. A spark plug 26 is installed at one side of the outlet of the mixing pipe 24, which, to ignite the gas-and-air mixture and thereby initiate a state of a gas combustion for generating the hot air to be guided into the inlet duct 12 by the guide funnel 20.
In the operation of a laundry dryer as constructed above, the blower 17 is actuated to drawn in the air in the drying chamber 5 via the lint duct 15, thus creating a pressure differential causing air to flow into the drying chamber via the inlet duct 12. The air flowing into the inlet duct 12 is heated to a high temperature by the gas combustion apparatus. Namely, gas is injected into the mixing pipe 24 via the gas nozzle 22, and the primary air flows into the inlet of the mixing pipe 24 to be mixed with the gas therein. The gas-and-air mixture is then ignited by the spark plug 26 provided at the outlet of the mixing pipe 24, and combustion begins. Heat energy generated from the combustion of the gas heats the air flowing through the guide funnel 20, i.e., secondary air, and the thus-generated hot air is supplied to the entrance hole of the inlet duct 12.
Referring to FIG. 3, the circular cross-section of the outlet end of the mixing pipe 24 produces a contiguous flame having a generally elongated shape. The diameter and length of the flame, as well as its separation from the outlet end of the mixing pipe 24, vary according to operational parameters of the blower 17, such as its rotational speed and exhaust resistance, determining a state of balance between the gas combustion and the inflowing air. If the speed of the blower 17 is properly controlled, a flame F is formed near the outlet end of the mixing pipe 24, but if the blower speed is too high, the resulting flame formation is a flame F′ separated (called “lifting”) from the outlet end of the mixed pipe. If the rotational speed of the blower 17 is too low, the resulting flame formation is excessively elongated. A long flame may reach into the inlet duct 12 to cause overheating or may even reach into the drying chamber 5 and cause a fire. Therefore, blower parameters must be carefully controlled to prevent an imbalance between the combustion rate of the gas and the amount of air intake. Such control of the blower is difficult, and failure may be catastrophic.
Moreover, the contiguous formation of the combustion flame F resulting from is circular cross-section of the outlet of the mixing pipe 24 limits the contact area between the flame and the secondary air entering the guide funnel 20. Heating efficiency is a direct result of size of the flame-to-secondary air contact area. The reduced contact area also results in incomplete combustion due to an insufficient supply of secondary air to the flame, which produces an elongated, yellow flame producing excessive amounts of soot and toxic gases such as CO, NOx, and SOx.
In addition, there is a tendency at the time of initial ignition by the spark plug 26 for the gas-and-air mixture within the mixing pipe 24 to escape from its outlet end, without combustion, thus lowering ignition capability.